Fuses, circuit breakers, and lambda diodes are known for protecting electrical circuits from spikes in current that could damage other components of the circuits. Fuses and circuit breakers, however, suffer from the disadvantage that they must be manually replaced or reset. Lambda diodes and devices derived from them unfortunately may introduce an undesirably high impedance in series with the load to be protected, and often require an auxiliary power supply to function properly. Sometimes that auxiliary power supply is provided by a battery or an independent circuit. If the auxiliary power supply fails, the protected circuit either no longer functions, or functions without adequate protection. The power consumed by a lambda diode may not impact a conventional low-power circuit; however, a high-power circuit will experience energy waste, shortened service life, and potentially significant thermal effects from conventional lambda diode configurations. Additionally, ultra-low power circuits such as so-called “nano-power” circuits, and various energy harvesting circuits are especially vulnerable to the effects of wasted energy.
Some lambda diode configurations also fail to take into account the significant variability in the performance characteristics of the transistors employed in the lambda diode. For example, the pinch-off voltage of standard manufactured junction gate field-effect transistors (“JFETs”) can vary considerably over a range of several volts, causing the lambda diode to block current at higher- or lower-than-expected currents. Other conventional configurations begin blocking current too quickly, because they are triggered by relatively harmless transient spikes. Still other configurations do not wait long enough before resetting and allowing current flow, potentially subjecting the protected circuit to still-dangerous overcurrents. Accordingly, a lambda diode configuration that does not account for those shortcomings will yield a device of questionable protective value.
Solid-state fuses other than lambda circuits usually appear as an integrated circuit and require at least one pin to be grounded. In this way, the solid-state fuse is partially in parallel with the load to be protected instead of entirely in series with that load. This reduces the effectiveness of those solid-state fuses. Further, the necessity of grounding the integrated circuit may restrict the placement of integrated power field effect transistors (“FETs”) to either high side or low side placement. Whichever placement is chosen, the additional burden is imposed of necessarily having to drive the potentials at the gates beyond the potential of the power rails. For higher-voltage applications especially, driving the gates above the high side rail or below the negative rail can be difficult and/or dangerous. In addition, solid-state fuses usually require a dedicated external power supply. Chaotic electrical conditions may cause power failure of the external power supply, resulting in the circuit to be protected being left unprotected. All of this reduces the effectiveness of those solid-state fuses.
Circuit protection devices are needed that do not require an auxiliary power source, more efficiently guard high-power circuit applications, adapt to high-side and low-side applications, serve any circuit with strict or sensitive energy requirements, and adequately protect electrical circuits.